[RPG] How powerful are mass mind control spells


I'm DMing a game where I want the BBEG to feel almost dreamlike: it can physically do little to nothing, but uses mind control and illusions.

Until now, it mind-controlled the mayor of a small town, hid objects from the players, blinked around a couple times, made a "time freeze illusion": I haven't thought through how powerful these things were because they just looked manageable for a high-level character so I figured they would be balanced.

For my next trick though, I'd like the guy to mind-control a small fortified village, with about 100 people in. Would this be balanced, story-wise?

  • By "balanced story-wise" I mean that I'm not concerned about the combat balance: I just don't want the players to think "the monster mind-controlled an ENTIRE VILLAGE? It must be too powerful for us to ever fight, we won't ever stand a chance".

  • By "mind-control 100 people" I mean that the village doesn't have a ruler, but after this spell the whole village sees the bad guy as their ruler: the town guards will protect him if needed, and everyone else just will just be sure that he's their righteous ruler.

  • I'm asking because I couldn't find a RAW mass mind-control spell, so I don't know how to check whether this would be feasible for a CR 20ish. What I'm looking for is something like "yes, this other monster can do similar things, you're good to go" or "not even a CR 20 monster could mind-control all those people, because Mind Control is a 7th level spell and a mass version would be too powerful".

Best Answer

With a sufficiently high spell save DC, a 20th level caster can get the entire town under their control in three and a half weeks.

This plan is going to use the spell geas:

You place a magical command on a creature that you can see within range, forcing it to carry out some service or refrain from some action or course of activity as you decide. If the creature can understand you, it must succeed on a Wisdom saving throw or become charmed by you for the duration. While the creature is charmed by you, it takes 5d10 psychic damage each time it acts in a manner directly counter to your instructions, but no more than once each day.

Geas, when upcast to 7th or higher, has this effect:

At Higher Levels. When you cast this spell using a spell slot of 7th or 8th level, the duration is 1 year. When you cast this spell using a spell slot of 9th level, the spell lasts until it is ended by one of the spells mentioned above.

The spell appears to give significant latitude to the caster in assigning the command, only specifying "some service". So a command like "obey me" or "do my bidding" appears to fit squarely within the spell's capabilities.

Now, for the numbers. A 20th level caster has four spell slots of 7th or higher, so four castings of geas per day for 25 days will get 25 of the townspeople under control indefinitely, and 75 of them under control for a year, assuming the caster's spell save DC is high enough to guarantee failure.

Therefore, it seems feasible within existing mechanics for a powerful spellcaster to control a town of 100 people.

Be advised, the townspeople might find it a bit...unnerving...when one of them drops dead for failing to follow your decrees:

While the creature is charmed by you, it takes 5d10 psychic damage each time it acts in a manner directly counter to your instructions

Surely he can come up with an explanation for this to maintain his positive image.

Challenge Rating: CR 20, possibly as low as CR 12.

As far as I can tell, the lowest CR creature with access to 9th level spell slots is the 18th-level Archmage at CR 12, with three 7th level or higher spell slots, so they could do it in 34 days. For 20th-level casters, the lowest CR is the Drow Matron Mother at CR 20.